US 3278864 A
Description (OCR text may contain errors)
Oct. 11, 1966 BUTLER 3,278,864
HIGH FREQUENCY POWER TRANSFER UNIT Filed June 28, 1960 2 Sheets-Sheet 1 Fig.3
Jesse L. Bufler INVENTOR W W ATTORNEY Get. 11, 1966 J, BUTLER 3,278,864
HIGH FREQUENCY POWER TRANSFER UNIT Filed June 28, 1960 2 Sheets-Sheet 2 2 72 i as 7 4 I 84 L 8 7g Fig. 5
Fig. 6 96 Jesse L.But|er INVENTOR fiWfi/W ATTORNEY United States Patent 3,278,864 HIGH FREQUENQY POWER TRANSFER UNIT Jesse L. Butler, Nashua, N.H., assignor to Sanders Associates, Iuc., Nashua, N.H., a corporation of Delaware Filed June 28, 1960, Ser. No. 39,286 4 Claims. (Cl. 333-) This invention relates to the art of high frequency transmission lines. More specifically, it relates to a system for transferring substantially all the power on one line to a second line unconnected thereto. The invention makes use of a pair of directional couplers connected in tandem, and it may be used to eliminate contacts in transmission line switches, and also to effect crossovers of signal paths in strip transmission lines without incurring crosstalk between the paths.
The directional couplers are connected in a novel fieldcancelling arrangement. If they are set for minimum coupling, all the input power on one line is transmitted through the device on the same line. If they are set at a 3 db coupling ratio, the entire power is coupled to another line.
Prior to the present invention, transmission line switches have been subject to all of the problems inherent in switches used in other applications. For example, the switch contacts tend to accumulate foreign matter such as dust and dirt in addition to the chemical products of switch arcing. These deposits, combined with normal wear of the contacts, often increase the contact resistance to the point where there is a significant voltage drop in the switch when appreciable current is passed through it. In low signal applications, contacts in this condition often develop objectionable noise.
Characteristic impedance is another problem in the case of transmission line switches. The characteristic impedance of the switch should be approximately the same as that of the transmission line to which it is connected in order to maximize transmission of energy through the switch. One way of meeting this difficulty has been to construct the switch with the same general configuration as the transmission lines with which it is to be used. Thus, a coaxial switch is often used with coaxial lines.
As will be seen below, the switching problem is closely related .to problems involving crossovers of signal paths. Most circuits having a fair degree of complexity require signal paths to cross over other signal paths without the transfer of energy from one path to the other. At low frequencies, this problem can easily be solved by use of a three dimensional construction. At higher frequencies where transmission lines are used and, more specifically, in the case of strip lines in which printed or etched circuits are used, a three dimensional crossover construction is relatively expensive to fabricate. Furthermore, it has a space requirement which works against the present day trend to miniaturization.
Accordingly, a principal object of my invention is to provide a transmission line switch free from the problems usually associated with switch contacts.
A mor specific object of the invention is to provide a switch construction compatible with strip transmission lines of the type described, for example, in US. Patents Nos. 2,810,892 and 2,812,501. The switch should be readily constructed with any desirable characteristic impedance so as to provide an impedance match with the transmission lines to which it is connected and thereby maximize the transmission of energy through it.
Another object of my invention is to provide an improved crossover adapted for the transposition of two transmission line signal paths.
A further object is to provide a crossover of the above 4 3,278,864 Patented Oct. 11, 1966 character disposed in a two dimensional layout and therefore adapted for construction by printed circuit techniques and incorporation in strip transmission lines.
A further object of the invention is to provide a switch and crossover of the above character which may be fabricated with relatively low cost techniques, while providing a high degree of reliability in operation.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comp-rises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.
In general, a crossover incorporating the features of my invention includes a pair of serially connected directional couplers, arranged so that the entire energy brought into the crossover on a first transmission line is coupled to a second transmission line. The two lines may be thought of as taking the configuration of a pair of Vs in the crossover, with the VS opening away from each other. A signal entering the crossover on one arm of one V leaves it on the diagonally opposite arm of the other V. Thus, speaking in terms of isolated signal paths, one path includes the portion of the first transmission line on one side of the crossover and the section of the second line on the opposite side thereof. The other sections of the first and second lines are in the other signal path extending through the crossover. The section of each transmission line in one signal path is electrically isolated from the section in the other path, even tho-ugh physically the two sections are parts of the same electrical conductors.
More specifically, my invention, which is adaptable to fabrication by printed circuit techniques and is thus well suited for use with strip transmission lines, comprises first and second directional couplers comprising portions of the lines. Each of the couplers has a 3 db coupling ratio, i.e., half the power entering a coupler on one line is transferred to the other line. The couplers are in series along the lines and are so arranged that, with a power input on one of the lines, the second coupler couples power in the same direction on the other line as the first coupler. The relative distances along the lines between the couplers are such as to provide field cancellation at the point where energy would otherwise leave the crossover on the transmission line on which it enters it.
Preferably, the directional couplers are parallel line couplers, and this is particularly important in switches made according to my invention, since such couplers require no physical connections between the transmission lines coupled thereby. Thus, effective switching openation may be obtained merely by moving the tnansmission line conductors between two poistions, one of which provides the above 3 db coupling ratio for transfer of all the energy on one tnansmission line to the other transmission line. The other position is one in which the tnansm-i-ss'ion line conductors are remote from each other, sothat there is essentially no coupling. In that case, all the energy is transmited through on the transmission line on which it enters the switch.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
FIGURE 1 is a simplified plain view, pantly broken away and partly in section, of a crossover lncorpona-ting the features of my invention,
FIGURE 2 is a cross section taken along line 4-4 of FIGURE 1,
line switch incorporating the features of my invention.
, 22 in this figure.
FIGURE 4 is a transverse sectional view taken along line '6 6 of FIGURE 3 and showing the relative positions of the conductors in one of the directional coupler-s incorporated therein,
FIGURE 5 is a schematic diagram ofa three-position switch made accord-ing ot my invention, and
FIGURE 6 is a transverse sectional view taken along line 8-8 of FIGURE 5 and showing the relative positions of the various conductors in one of the directional couplers therein.
Referring now to FIGURE 1, a crossover made according to my invention is preferably constructed in a strip line configuration and thus is sandwiched between a pair of ground plane conductors, one of which is indicated at A center conductor 24 is disposed in the upper surfia-ce of an insulator =26 bonded to the ground plane conductor 22. A second center conductor 28 is disposed in the lower surface of an insulator 30', facing the insulator 26. The conductors 24 and-28 are in close proximity to each other in a pair of parallel line directional couplers generally indicated at 32 and 34.
FIGURE 2 is a cross section taken through the directional coupler 34. As shown therein, a second ground plane conductor 36 is bonded to the upper surface of the insulator 30. The center conductors 24 and 28 are disposed in recessesin the insulators 26 and 30 in order to provide clearance between these conductors in the directional couplers 32 and 34 (FIGURE 1) where they are more or less in registration. For the purpose of clarity, the relative dimensions of the various parts are exaggerated in the drawings and particularly in FIGURE 2. Actually, the center conductors 24 and 28 may be thin films, and, thus, with minimum clearance between them, they may both be considered to be disposed midway between p-l ane conductors 22 and 36.
The directional couplers 3'2 and 34 should have a coupling ratio of 3 db. That is, one-half the input energy on one line is coupled to the other line forming the coupler, and one-half is transmitted through the coupler on the input line. It will be appreciated that, to realize this coupling ratio, the exact positions of the center conductors over each other will vary, depending upon the vertical spacing between them. More specifically, in many cases they may not be in exact registration with each other.
The operation of the crossover of FIGURE 1 is as follows, keeping in mind that the directional couplers 32 and 34 are nominally a quarter wavelength long; and that the coupled output is propagated in a direction opposite to the input and in phase therewith, while the transmitted output lags the input by a phase angle of 90 degrees. Assume that the center conductor segments 24a and 28a extending between the couplers 32 and 34 are of equal length. Then, if energy enters the crossover by way of the transmission line including the center conductor segment 28b, the coupler 34 will split this energy evenly into two portions travelling toward the coupler 32 along the line segments 24a and 28a. The energy on the segment 24a arrives at the coupler 32 at a phase angle of 90 degrees ahead of the energy arriving at this coupler on the segment 28a. One half the energy arriving at the coupler 32 on the segment 24a is coupled to the conductor 28 toward the segment =28c thereof. Also, one-half the en-.
ergy arriving at the coupler on the segment 28a is transmitted along the line 28 toward the segment 280. This latter energy undergoes an additional 90 degrees phase delay in'travellin-g through the coupler and therefore arrives at the segment 280 180 degrees out of phase with the energy coupled thereto irom the segment 24a. Since the two constituents of the energy entering the segment 28c are in phase opposition and have equal amplitudes, they cancel, :and, therefore, no energy is transmitted along that segment. Accordingly, tall the energy entering the coupler 32 leaves it by way of the segment 24b.
Thus, I may define a signal path A as shown in FIG- URE 1, which extends through the crossover by way of the center conductor segments 28b 24!). Similarly, a
signal path B extends through the crossover on segments 28c and 240. Energy entering the crossover on the segment 28c will undergo cancellation at the segment 28b in the manner described above, and, therefore, all of it will leave the crossover by way of the segment 240. It will be apparent that the operation will be similar when energy proceeds along the two signal paths in directions opposite to those indicated by the arrows. Thus, there is complete isolation between the two signal paths, although they cross over each other between the same pair of ground planes and also in spite of the tact that the signal includes portions of the same center conductors.
The lengths of the segments 24a and 28a may differ by any integral number of wavelengths for operation in the manner described above. However, the crossover will be less frequency sensitive if the difference is zero, i.e., the lengths are equal. Furthermore, it should be understood that a parallel line directional coupler may have a nominal length of any odd number of quarter wavelengths. Where this number is greater than one, the phase difference between the coupled and transmitted outputs of a coupler may be other than the 90-degree value assumed above. In such case, the relative lengths of the line segments between the couplers can be adjusted to provide the field cancellation characteristic of my invention.
It will be noted that, in the directional couplers 32 and 34, the center conductors 24 and 28 are somewhat narrower than along other portions of these conductors. The reason for this is that, in the couplers, each conductor increases the efiective capacitance between the other conductor and the ground plane conductors 22 and 36 1t h ereby changing the characteristic impedances of the transmission line in the couplers. This effect is compensated for by reducing the sizes of the center conductors and thereby reducing the line capacitances to a point where there is no change in characteristic impedance as a line enters a coupler.
The center conductors of a switch made according to my invention are illustrated in FIGURE 3. As shown therein, a pair of center conductors 38 and 40, disposed between a pair of ground planes (not shown in FIGURE 3), are brought into proximity to each other in a pair of variable directional couplers generally indicated at 42 and 44. The variable couplers 42 and 44 may be of the type described in the copending application of Donald R. Ayer, for Variable Directional Coupler, Serial No. 35,102, filed May 10, 1960, noW Patent No. 3,095,544,
and assigned to the assignee of this application. As described therein, a mechanism may be provided for moving the center conductors in a coupler toward and away from each other to vary the degree of coupling between them. Thus, as seen in FIGURE 3, the center condoctors 38 and 40 are sufliciently far enough apart in the couplers 42 and 44 to virtually isolate the conductors from each other. Accordingly, in this position of the switch, energy entering the line segment 38a will be completely transmitted through the couplers 42 and 44 on the conductor 38 to leave the switch by way of an output segment 38b.
In the other position of the switch of FIGURE 3, the conductors 38 and 40 are close enough together to provide 3 db coupling ratios in both the couplers 42 and 44. Assuming that the line segments 38c and 40a between the couplers have the proper relative lengths discussed above, operation of the unit will correspond to that de scribed for the crossover of FIGURE 1. With field cancellation at the segment 38b, all the input power will be coupled to the transmission line including the conductor 40 and appear at the output segment 4%. Thus, by moving the conductor 38 between two positions, the input power on the segment 38a may be delivered entirely to the segment 38b or the segment 4011. It will be noted that this operation requires no making and breaking whatsoever of physical contacts between various conductors.
The variable couplers 42 and 44 preferably also include compensators 46, 48, 50, and 52, which maintain the characteristic impedances of the transmission lines constant regardless of the position of the switch of FIG- URE 3. More specifically, as noted above, the conductors 38 and 40 have diminished widths in the coupler 42 in order to eliminate discontinuities in the characteristic impedances of the transmission lines when the coupler is arranged for maximum coupling, i.e., when the lines 38 and 40 are closest to each other. Without the compensators 46 and 48, the capacitances of these sections of the conductors 38 and 40 would be less than in the other portions of the transmission lines when the couplers are positioned, as in FIGURE 3, for minimum coupling. This effect is offset by the relative motions of the conductors 38 and 40 and the compensators 46 and 48, which preferably take the form of short sections of conductor formed in the same manner as the transmission line center conductors.
More specifically, compensator 46 is mechanically connected to the conductor 38, and, thus, as the latter conductor moves away from the conductor 40, the conductor 46 moves toward it. The capacitance added by the compensator 46 is just enough to compensate for the decrease in capacitance of the line 40 in the coupler 42 caused by withdrawal of the conductor 38. Similarly, as the conductor 38 moves away from the conductor 40, it approaches the compensator 48, which serves to increase its capacitance. The compensators 50 and 52 in the coupler 44 operate in the same manner.
FIGURE 4 is a fragmentary cross section taken through a switch including the coupler 42. The inner conductor 38 and compensator 46 are secured in an insulator 54 disposed within a housing member 56. Similarly, the conductor 40 and compensator 48 are bonded to an insulator 58 in a housing member generally indicated at 60. The members 56 and 60 include outer plates 62 and 64 which provide the functions of ground plane conductors, as well as side walls 66 and 68, which have engaging surfaces 66a annd 68a and thus provide the functions of the shorting pins.
In the full line position of FIGURE 4, the couplers 42 and 44 of FIGURE 3 are in the disengaged position shown in the latter figure. To change the position of the switch, the member 56 is moved to the left (FIG- URE 4) into the dotted line position to provide a 3 db coupling ratio in each of the directional couplers.
FIGURE 5 illustrates schematically a three position switch incorporating the principles of my invention. A center conductor 72 is arranged for reciprocation between a pair of center conductors 74 and 76 in double variable directional couplers generally indicated at 78 and 80. The lengths of the conductors 72, 74, and 76 between the couplers 78 and 80 are as given above. Accordingly, with the conductor 72 positioned for a 3 db coupling ratio with the conductor 76 in the couplers 78 and 80, energy entering the switch at the terminal 82 will leave it by way of the terminal 84 on the conductor 76. If the conductor 72 is moved to a position midway between the conductors 74 and 76, it will be too far from both of them for energy to be coupled to either of them. Accordingly, the output of the switch will then appear at the terminal 86 on the conductor 72. When the conductor 72 is moved into proximity with the conductor 74 to provide a 3 db coupling ratio therewith in each of the directional couplers, all the input energy is delivered to the terminal 88 of the conductor 74.
FIGURE 6 illustrates the cross section of a three position switch of the type shown in FIGURE 5. The conductors 74 and 76 are bonded to insulators 98 and 92 in housing members 94 and 96. The conductor 72 is disposed in an insulator 98 attached to metallic ferrules 100 disposed between and engaging the members 94 and 96. Operation of the unit is accomplished by translation of the insulator 98 and ferrules 100 to bring the conductor 72 into one of the three positions corresponding to a 3 db coupling ratio with either the conductor 74 or 76, or midway between the two couplers, as described above. Thus, I have described an improved signal path crossover for use in transmission line systems, particularly those using thin film conductors formed by conventional printed or etched circuit techniques. The crossover combines a pair of 3 db directional couplers connected in a novel tandem arrangement to interchange the signals transmitted on a pair of transmission lines. In accordance with the invention, a signal entering the crossover on one of two transmission lines leaves it on the other line.
My invention is also of use in transmission line switches, such as those described above, wherein an input signal on one transmission line may be made to transfer to another line in the same manner as the interchange is effected in the stationary crossovers. Switching is accomplished by moving the directional couplers between the 3 db position and another position in which the two transmission lines therein are virtually isolated from each other. In that case, the energy entering the switch leaves it on the same line instead of being transferred to another line.
It will thus be seen that the objects set forth above, among those made apparent fromthepreceding description, are efliciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
What is claimed is:
1. A transmission line switch comprising first and second center conductors substantially centrally disposed between a pair of parallel ground plane conductors in a strip line configuration, a first unit including said first center conductor, said first ground plane conductor and a first insulator disposed therebetween, a second unit comprising said second center conductor, said second ground plane conductor and a second insulator disposed therebetween, a pair of directional couplers including portions of said center conductors and in series therealong, said first unit being movable with respect to said second unit to provide for variation of the coupling ratio of said directional couplers between a first position in which there is essentially no coupling and a second position providing a 3 db coupling ratio, said couplers being so connected that with input power on the transmission line including one of said center conductors said first coupler couples power in the other of said transmission lines in the same direction as said second coupler, the distances along said lines between said couplers being such as to provide substantial field cancellation at the point where energy would otherwise leave the second coupler through which it passes on the transmission line on which it enters said switch when said switch is in said second position.
2. The combination defined in claim 1 in which each of said couplers provides a phase difference of degrees between the output terminals from which energy emerges when said switch is in said second position, the distances along said center conductors between said couplers differing by n wavelengths where n is an integer including zero.
3. A transmission line switch comprising first, second and third center conductors substantially centrally disposed between a pair of ground plane conductors in a strip line configuration, a first unit comprising said first center conductor, said first ground plane conductor and a first insulator disposed therebetween, a second unit comprising said second center conductor, said second ground plane conductor and a second insulator disposed therebetween, a third unit including said third center conductor and means movably mounting said third conductor between said first and second units in spaced relationship from said first and second center conductors, first and second center conductors extending toward said third center conductor, said third center conductor disposed between each of said couplers including portions of said first and second center conductors extending toward said third center conductor, said third center conductor disposed between said portions, said third unit being disposable in a first position in which said third center conductor is essentially isolated from said firs-t and second center conductors, a second position in which there is a 3 db coupling ratio between said third and first oenter conductors in said directionalcouplers and a third position in which there is a 3 db coupling ratio between said third and second center conductors, said couplers being so arranged that with input power on the transmission line including said third center conductor said first coupler couples power in the same direction on a transmission line including one of the other of said center conductors as said second coupler when said third unit is in said second and third positions, the relative distances along said lines between said center conductors between said couplers being such as to provide substantial field cancellation at the point where energy would otherwise leave said third center conductor when said third unit is in said second and third posit-ions.
4. In a high frequency power transfer unit adapted to transfer from a first transmission line to another transmission line substantially all the power entering said unit on said first line, the combination of first and second directional couplers comprising portions of said lines, said coupler-s being in series along said lines and being so arranged that with input power on one of said lines, said first coupler couples power in the same direction on the other of said lines as said second coupler, the relative distances along said lines between said couplers being such as to provide substantial field cancellation at the point where energy would otherwise leave said unit on the same line and in the same direction by which it enters said unit when said couplers have a 3 db coupling ratio, and means for varying the coupling ratio of said couplers between positions providing 3 db coupling ratio and a position providing essentially no coupling, whereby energy entering on one of said lines may be switched between the line on which it enters and the other of said lines.
References Cited by the Examiner UNITED STATES PATENTS 2,531,777 11/1950 Marshall 333 10 2,586,993 2/1952 Riblet 330 10 2,704,351 3/1955 Dicke 333 11 FOREIGN PATENTS 950,304 10/1956 Germany.
OTHER REFERENCES Barrett: Etched Sheets Serve as Microwave Components. Electronics, June 1952, pages 114 to 118.
Shimizu: Stripline 3 db Directional Couplers, 1957, IRE Wescon Convention Record, vol. 1, part 1, pages 4-15.
HERMAN KARL SAALBACH, Primary Examiner.
ELI J. SAX, Examiner.
C. H. SCHWARTZ, Assistant Examiner..
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,278,864 October 11, 1966 Jesse L, Butler It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 2, line 53, for "poistions" read positions line 59, for "transmited read transmitted column 3, line 6, for "ot" read to column 7, lines 6 and 7, strike out "center conductors extending toward said third center conductor, said third center conductor disposed between" and insert instead parallel line directional couplers including said center conductors and connected in series along them,
Signed and sealed this 5th day of September 1967 (SEAL) Attest:
ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents